Anti-pick lock device



Oct. 12, 1965 N. R. ADLER ANTI-PICK LOCK DEVICE Filed Dec. 5, 1963 I mm A m n" II I I NVENTOR.

IVO/F/f/M/ A. 14015? United States Patent 3,210,974 ANTI-PICK LOCK DEVICE Norman R. Adler, Fitchburg, Mass., assignor to Iu- This invention relates to an anti-pick lock device, and more particularly to a lock device which is resistant to tampering or picking of a particular form known as rifiiing.

A common difiiculty encountered in the preservation of the security of a series of locks of a given keyway section lies in the susceptibility of a lock or locks of such series being picked through the use of a key bitted to fit a diiferent one of the series. The technique employed to pick a lock under these circumstances, commonly referred to as rifliing, is practiced by shifting a key whose keyway section matches the keyway section of the lock to be picked but whose bitted combination is different from that of such lock, repeatedly forwardly and rearwardly within the keyway while applying a constant torque to the key. Such technique depends upon angularly shifting the tumbler bores of the rotatable plug slightly out of registry with the tumbler bores of the casing through the application of a torque to the key. When the parts mentioned are disposed in the slightly out of registry position, and the key is rapidly shifted inwardly and outwardly, the lowermost edges of the driver pins tend, upon being pressed outwardly of the casing, to hang or engage against portions of the outer periphery of the plug which have been disposed beneath the driver pins by the application of torque to the key. With repeated inward and outward strokes of the key, the driver pins are progressively caused to hang and, of course, when each of the pins rests against the outer periphery of the plug rather than descending into the cross bore portions of the plug, the plug may be rotated to the unlocked position.

Various means have been proposed for protecting pin tumbler locks from efforts to pick them using the riffiing technique. Such means usually involve providing pins or the casing or the plug with unusual configurations or shapes to prevent the hanging of the pins. While such structures have been successful in a measure, the complexity of the preparation of the casing, pins or plug has rendered their use applicable only in high priced, high security locks and lock sets.

Accordingly, it is an object of the present invention to provide a rifile-resistant lock assembly which does not involve extraordinary manufacturing procedures and which is simple and inexpensive to manufacture.

A further object of the invention is to provide a riflieresistant lock assembly which may be of the pin tumbler or wafer tumbler type which will resist picking by the riffling method through the use of a key having the same keyway section but a different combination from the key for said lock.

To attain these objects and such further objects as may appear herein or be hereinafter pointed out, I make reference to the accompanying drawings, forming a part hereof, in which:

FIGURE 1 constitutes a bottom view of a lock assembly in accordance with the invention, a key being shown in place in the lock;

FIGURE 2 is a vertical section taken on the line 2--2 of FIGURE '1;

FIGURE 3 is a section taken on the line 33 of FIG- URE 2;

FIGURE 4 is a section comparable to FIGURE 3, showing a prior art device;

FIGURE 5 is a fragmentary perspective view of the leading portion of a key for operating the lock of the present invention, the key being shown in inverted position.

In accordance with the invention, a pin tumbler lock mechanism 10 is provided with a casing 11 wherein there is rotatably mounted a cylindrical plug 12, the outer periphery of which plug rotates within main bore 13 formed in the casing 11. The casing 11 is provided with the usual radially extending cross bores 14, which cross bores, in the locked position of the device, register with cross bore extensions 15 formed in the plug 12. The plug incorporates a longitudinally extending keyway 16 which intersects the cross bore extensions 15 of the plug 12.

In the usual manner, there is disposed in the cross bores 14, driver springs 17 having their lower ends biased against driver pins 18. The cross bores 14 and cross bore extensions 15 are additionally provided with follower pins 19.

In the locked condition of the mechanism, the springs 17 press the driver pins 18 across the shear line between the plug and the casing, thus causing the driver pins to span the shear lines and the follower pins 19 to be disposed entirely within the cross bore extensions 15. This condition of the lock is best shown in FIGURE 3.

In accordance with the invention, that portion of the under surface of the casing 11 which is in alignment with the plane intersecting the axes of the cross bores 14 is cut away or opened, as best seen in FIGURES 1 and 2, to define what amounts to a longitudinally extending slot 20 in the under surface of the casing. The slot 20 may include a relatively narrow entrance portion 21.

In the illustrated embodiment, forward and rearward shifting movement of the plug in respect to the casing is prevented by a limit pin 22, which pin rides in an arcuate groove formed part way around the casing, thereby serving in addition to limit the rotary movement of the plug and easing. It will be readily understood that other means for effecting one or both of these functions, each as a snap washer, etc. may be employed.

The lock in accordance with the invention is provided with a key K which, in addition to the usual upper bitted surface 23, is provided with a depending lug 24 which extends a slight distance below the lowermost edge 25 of the key. In the illustrated embodiment, the degree of extension of the lug beneath edge 25 has been somewhat exaggerated for clarity, and it will be understood that in commercial production, the lug need only be of a size to provide the function hereinafter set forth.

The key K, which is properly mated to the combination of the illustrated lock embodiment, is shown in position in FIGURE 2. As seen therein, the junction of the driver pins 18 and follower pins 19 is exactly aligned with the shear line, i.e. at the height of the outer periphery of the plug 12. The lug 24, in the fully inserted position of the key, clears the innermost end 26 of the casing so that the key may be rotated without interference between the lug 24 and the casing.

The under surface of the plug forms a continuous open groove, as best seen from FIGURE 3.

The height of the lug 24 is such that upon insertion into or removal of the key K from the keyway, the lug 24 projects through the groove in the under surface of the plug and into the slot 20' defined on the lower surface of the casing. Further, the transverse dimension of the lug 24 is such that it closely approximates the corresponding dimension of the slot 20, and particularly the innermost portion 21 of said slot.

From the foregoing it will be seen that upon insertion or removal of the key K into or from the plug, the lug 24 will lie within a portion of the slot 20 of the casing.

The disposition of the lug of the key in the slot of the casing, by reason of the close tolerances between theseparts and the particularly close tolerance of the lug with the innermost part 21 of the slot, results in the establishment of a rather precise angular orientation of the plug with respect to the casing each time the key is at an intermediate inserted position. The net result of this relationship of the lug and the slot is precisely to align the axes of the cross bores 14 with the cross bore extensions 15 each time the key is inserted or withdrawn.

In FIGURE 4 there is shown in somewhat exaggerated form a lock in accordance with the prior art wherein a driver pin 18a has its lowermost end 18b hung up or lying against a portion of the periphery ofthe plug 12a. It will be noted from FIGURE 4 that the plug is partially angularly rotated with respect to the casing, resulting in a slight out of registry position of the cross bore portions of the plug and casing. It is this out of registry condition which must be achieved in order successfully to pick a lock through the riffling method.

In the lock of the present invention, however, an engagement of the lug and the slot in the casing serve to center the plug and easing with each shifting movement of the key. Any attempt to apply torque to a key in the lock of the present invention will be ineffective to induce the partially out of registry condition shown in FIGURE 4 since a relative rotation of the plug and easing can be achieved only at the fully inserted position of the key with respect to the plug, i.e. where the lug 24 clears the casing. Should an attempt to apply torque to the key at an intermediate inserted position be made, the degree of rotation of the plug is limited by the tolerance between lug 24 and slot 20, which is less than the degree of rotation permitted by the tolerances between the driver and follower pins and the respective tumbler bores.

The device of the present invention is particularly useful where a large number of lock units, such as padlocks, are issued, the locks in each unit differing from each other only in the pin tumbler combination.

By means of the foregoing invention, a simple expedient is provided which will prevent one key of a series from operating a different lock in the series as a result of rifiling.

Having thus described the invention and illustrated its use, what is claimed as new and is desired to be secured by Letters Patent is:

1. A lock mechanism comprising a housing having a main bore, a plug rotatably mounted in said bore of said housing, a longitudinally extending keyway formed in said plug, a cross bore extending radially from said housing into said plug and intersecting said keyway, a slot formed in the under surface of said plug in communication with said keyway and opening onto said main bore, locking tumblers disposed in said cross bore and shiftable radially to locking and unlocking positions of said plug, a groove formed in said housing and registering with the slot of said plug in the locked position of said plug, key means for said lock including a bitted edge for shifting said tumblers to the unlocking position of said plug when said key is fully inserted into said keyway, a depending lug on the edge of said key opposite said bitted edge, said lug being of a height to extend through said slot of said plug and into the groove in said housing in all partially inserted positions of said key in said plug, and a clearance portion formed in said housing positioned to lie adjacent said lug in said fully inserted position of said key, said clearance portion permitting relative rotation of said plug and housing.

2. In a lock mechanism wherein a lock plug having a keyway is rotatably mounted in a housing having a main bore, a slot defined in said plug communicating with said keyway and opening onto said bore, a groove defined by said housing in registry with said slot of said plug in the locked position of said plug, a key insertible into said keyway of said plug and including a lug extending radially beyond said slot and into said groove in all partially inserted positions of said key into said keyway, said housing providing clearance for said lug in said fully inserted position whereby said plug may be rotated to unlocking position without interference between said lug and said housing.

3. A lock mechanism in accordance with claim 1 wherein the cross sectional thickness of said lug approaches with close tolerances the cross sectional dimen- References Cited by the Examiner UNITED STATES PATENTS 9/96 Donovan 340 8/57 Schlage 7042Q ALBERT KAMPE, Primary Examiner, 

2. IN A LOCK MECHANISM WHEREIN A LOCK PLUG HAVING A KEYWAY IS ROTATABLY MOUNTED IN A HOUSING HAVING A MAIN BORE, A SLOT DEFINED IN SAID PLUG COMMUNICATING WITH SAID KEYWAY AND OPENING ONTO SAID BORE, A GROOVE DEFINED BY SAID HOUSING IN REGISTRY WITH SAID SLOT OF SAID PLUG IN THE LOCKED POSITION OF SAID PLUG, A KEY INSERTIBLE INTO SAID KEYWAY OF SAID PLUG AND INCLUDING A LUG EXTENDING RADIALLY BEYOND SAID SLOT AND INTO SAID GROOVE IN ALL PARTIALLY INSERTED POSITIONS OF SAID KEY INTO SAID KEYWAY, SAID HOUSING PROVIDING CLEARANCE FOR SAID LUG IN SAID FULLY INSERTED POSITION WHEREBY SAID PLUG MAY BE ROTATED TO UNLOCKING POSITION WITHOUT INTERFERENCE BETWEEN SAID LUG AND SAID HOUSING. 